Solvent recovery by charcoal adsorption and steam desorption



United States Patent Y 3 Claims. ci. 202-170 The present invention relates to an apparatus for recovering solvents, particularly perchloroethylene and trichloroethylene, by absorption on activated charcoal and desorption by means of flushing with steam.

Known arrangements of this type work by operating activated charcoal filters either singly on alternately, one filter ora group of filters being used for adsorption in the latter case while the other filter or group of filters is used for desorption. For this purpose the filter chambers are alternately connected to a suction pipe for the air which is to be cleaned and which contains the solvent, and through a steam pipe to a source of steam for desorption by steam flushing.

In addition it is known for the steam to be superheated before entering the filter chamber. In these known arrangements the steam generator, the superheater, and the filter are connected together by piping. This is disadvantageous both from the point of view of construction and from the point of view of operation. Separation of the various parts of the plant has on the one hand the consequence that the steam generator must comply with the regulations for the supervision of steam workers, while in addition this separation gives rise to unnecessarily high steam consumption and inconvenience tends to be caused by fluctuations resulting from loading by other steam consumers, when the steam boiler, as is frequently the case, is connected to other loads. In the design of the steam generator and also of the superheater, the losses occurring in the steam pipes must moreover be taken into account. The question of the economy of the recovery of perchloroethylene and trichloroethylene depends both on steam consumption and on the expense of apparatus. In order to reduce these two cost factors, the present invention is based on the consideration that in the desorption process the activated charcoal chamber offers only such little resistance to the passage of the flushing steam that the container forming the filter chamber can in practice be regarded as an open container for the purpose of the steam boiler regulations, so that it is not subject to those regulations.

According to the invention, this circumstance can be 1 utilised both to reduce the steam consumption and to reduce the cost of apparatus by connecting the chamber containing the activated charcoal at the bottom directly to an evaporation vessel open at the top and containing a heater, while a superheater may also be disposed in the steam chamber of the vessel. Not only is the effect thereby achieved that each individual filter forms a selfcontained unit with its steam generator and superheater, but in addition since the steam generator together with the filter now forms a practically open vessel, the entire unit can be designed without having to bear the burden of respecting the steam boiler regulations, while at the same time through the reduction of the heat losses in the connecting steam pipes and through the optimum adaptation, which is now possible in a particularly simple manner, of the properties of the flushing steam to the task of recovery it is possible to achieve a reduction of steam consumption. The production of the flushing steam directly beneath the filter chamber also provides the advantage that in this way particularly favourable evapo- 3,332,854 Patented July 25, 1967 ice ration conditions are achieved with an agreeably low elevated pressure.

In recovery plants of the type referred to, it is very important to keep the solvents away from any part having a high temperature, because otherwise dangerous chemical reactions may take place. This circumstance may :also be one of the factors which gave rise to the separation of the steam generator and superheater from the filter chamber. In order to eliminate harmful chemical actions through the excessive heating of solvents despite the constructional combination of the steam generator and superheater with the filter chamber, according to the invention there may be disposed between the evaporation vessel and the filter chamber an interception device which prevents particles of activated charcoal with solvents from passing into the superheater and steam generator.

One form of embodiment of the invention is described hereinbelow with reference to the accompanying drawing.

The drawing shows a longitudinal section of an appa ratus according to the invention, serving for the recovery of solvents, particularly perchloroethylene and trichloroethylene, such as is used in chemical purification plants and also in industrial metal degreasing plants, for chemical cleaning in the textile industry, and also in the extraction industry for the recovery of oils, and the like. The plants serve not only to recover solvents, but also to purify the surrounding atmosphere.

Suction is applied through a piping system, adapted to individual circumstances, to the apparatus working with these solvents, and the mixture of gas and air is forced through an inlet pipe 1 into a filter chamber 2 contain- -ing activated charcoal 3 and, after passing through the activated charcoal filling and giving up the major part ,in both the air inlet and air outlet pipes, and the plant is changed over from adsorption operation to desorption operation. For this purpose an electrically heated steam generator 6 is connected directly to the bottom of the filter chamber 2, said steam generator consisting of a bottom water chamber 7 in the form of a pot having for example a rectangular ground plan, and a steam chamber 8 lying thereabove and open at the top.

An electric immersion heater 9, which is connected to terminals 10, is provided in the water chamber 7 for heating purposes. Above the water chamber there is provided an electric heater 11 which extends substantially over the free cross-section of the chamber and which is connected to terminals 12 and serves to superheat the steam. The heaters 9 and 11 may be connected to the supply mains through a common switch.

For the purpose of regulating the supply of water and the water level 13 in the steam generator, a float regulator 14 is provided in the usual manner and is made fast to the container of the steam generator and in communication with the steam chamber of the steam generator through a pressure equalisation pipe connected above the level of the water.

During adsorption operation the steam chamber 8 serves as an outlet chamber for the purified air; the air outlet pipe 4 is disposed in the cylindrical wall of the steam chamber.

The filter chamber 2 and steam generator 6 are detachably connected together by a flange connection 15.

Above the heater 11 a condensate interceptor 16 is installed. This consists of a circular cup 17 and a diaphragm or drip plate 18 lying a certain distance above the cup 17 and covering the free passage aperture of the cup 17 in such a manner that condensate forming from the activated charcoal filter or falling through the activated charcoal carrier sieve 19 is intercepted by the drip plate 18 and passes over its edges into the cup 17. The cup 17 may be connected to an outlet, not shown in the drawing. During the desorption operation by flushing with steam, the heaters 9 and 11 are adjusted independently of one another in such a manner that steam passes into the filter chamber 2 with a certain degree of superheating, which is adapted to working conditions and the properties of the solvent used. The steam pressure is also adapted to individual circumstances, particularly to the flow resistance in the activated charcoal filter, by adjusting the heaters. The heater 9 is automatically switched off if the supply of water fails or is interrupted.

As it passes through the activated charcoal, the superheated steam entrains the adsorbed solvent and passes by way of a dome 20 which is provided on the top of the filter chamber, and to which the supply pipe 1, now closed, for the air to be purified in the adsorption phase, and a pipe 21 into a condenser 22 in which steam and solvent condense. Through their difierent specific gravities the condensates are separated from one another in a known manner in the separator 23 and discharged through condensate pipes 24 and 25. The solvent thus recovered is passed direct to the cleaning plants for reuse or to storage tanks for later reuse.

In order after the evaporation to obtain the quickest possible cooling, which is important to the adsorptive capacity of activated charcoal, the heated water is run out of the steam generator through a three-way valve 26. After changing over this valve again, the steam generator is automatically filled with cold water, so that the heating elements are practically continuously under water and thus not exposed to the corrosive influence of solvent gases.

The heating and the discharge of steam are coupled to one another in such a manner that through an interlock device 27 between the outlet valve 28 and the heating switch 29 the heater 9 is switched on only when the container is open.

The switches and valves 5, 5, 26, 28 and 29 can be operated by a single common handle, in order to pass from desorption to adsorption operation and vice versa. This changeover may also be made automatically, preferably in accordance with a predetermined adjustable time function, or be controlled by an instrument measuring the concentration of the solvent. The pressure in the steam chamber Sis determined by the resistance of the filter charcoal 3 and of the outlet pipe. It will not exceed the value of 0.3 atmospheres gauge. The superheating is so adjusted and controlled that the maximum permissible temperature for the solvent used is not exceeded.

Various modifications and other embodiments are also possible within the scope of the invention; in particular,

the steam generator could also be provided with another heating system instead of electric heating, although because of its simplicity and ease of operation electric heating is generally to be preferred. In addition the plant can be provided with the usual safety devices.

I claim:

1. An apparatus for recovering solvents such as perchloroethylene and trichloroethylene by adsorption on activated charcoal and desorption by flushing with steam,

said apparatus comprising means defining a chamber containing activated charcoal including a charcoal carrier sieve,

a first gas conduit means located on one side of said chamber and communicating therewith and a second gas conduit means located on an opposite side of said chamber and communicating therewith,

an evaporation vessel opened at its top facing said carrier sieve and having gas flow communication therewith,

a steam generator heater positioned in said vessel,

superheating means positioned below said sieve and above said steam generator heater,

and interception means positioned between said steam generator heater and said sieve above said superheating means to intercept materials passing downwardly from said chamber toward said heater.

2. An apparatus in accordance with claim 1 wherein said steam generator heater is submerged and said interception means is a drip baffle plate having a circular cup arranged about the periphery of said plate for receiving and collecting condensate.

3. An apparatus in accordance with claim 2 wherein said sieve is on a bottom side of said chamber and a steam conduit is positioned above and communicating with said chamber.

References Cited UNITED STATES PATENTS 1,504,588 8/1924 Tunison 202--169 X |1,863,803 6/1932 Patenburg 20349 X 1,986,165 1/1935 Sieck 202-159 X 2,459,951 1/ 1949 Metzner 203-49 X 2,801,958 8/1957 Fortenbacher et al. 202170 2,816,064 12/ 1957 Smith a- 203-10 3,089,250 5/ 1963 Victor 203- X 3,177,126 4/1965 Charreau 202-470 X 3,183,649 5/1965 Teller 5571 3,224,168 12/1965 Gregory 11208 X FOREIGN PATENTS 1,209,244 2/ 1960 France.

NORMAN YUDKOFF, Primary Examiner. F, E. DRUMMOND, Assistant Examiner, 

1. AN APPARATUS FOR RECOVERING SOLVENTS SUCH AS PERCHLOROETHYLENE AND TRICHLOROETHYLENE BY ADSORPTION ON ACTIVATED CHARCOAL AND DESORPTION BY FLUSHING WITH STEAM, SAID APPARATUS COMPRISING MEANS DEFINING A CHAMBER CONTAINING ACTIVATED CHARCOAL INCLUDING A CHARCOAL CARRIER SIEVE, A FIRST GAS CONDUIT MEANS LOCATED ON ONE SIDE OF SAID CHAMBER AND COMMUNICATING THEREWITH AND A SECOND GAS CONDUIT MEANS LOCATED ON AN OPPOSITE SIDE OF SAID CHAMBER AND COMMUNICATING THEREWITH, AN EVAPORATION VESSEL OPENED AT ITS TOP FACING SAID CARRIER SIEVE AND HAVING GAS FLOW COMMUNICATION THERE WITH, A STREAM GENERATOR HEATER POSITIONED IN SAID VESSEL, SUPERHEATING MEANS POSITIONED BELOW SAID SIEVE AND ABOVE SAID STEAM GENERATOR HEATER, AND INTERCEPTION MEANS POSITIONED BETWEEN SAID STEAM GENERATOR HEATER AND SAID SIEVE ABOVE SAID SUPER HEATING MEANS TO INTERCEPT MATERIALS PASSING DOWNWARDLY FROM SAID CHAMBER TOWARD SAID HEATER. 